RNA from the type strain of turnip mosaic virus (TuMV), a member of the potyvirus group, was translated in either rabbit reticulocyte lysate or wheat germ extract. We found no evidence for encapsidated, subgenomic TuMV RNA species. A broad size range of -[S]methionine-labelled polypeptides with molecular weights up to 200 000 (200K) was observed in TuMV RNA-programmed reticulocyte lysates. In contrast, a single polypeptide of 44K predominated in the much narrower spectrum of labelled products, of 55K or less, seen in wheat germ extracts containing TuMV RNA. Time course experiments revealed that, in rabbit reticulocyte incubations, many of the low molecular weight TuMV RNA-encoded polypeptides accumulated only after synthesis of the largest polypeptides (i.e. those ⩾ 100K). When the amino acid analogues -fluorophenylalanine, -canavanine and -tosyl-lysyl-chloromethane were substituted for phenylalanine, arginine and lysine respectively, the major 44K product detected in wheat germ extracts diminished, to be replaced by a product of 92K which co-migrated with the major polypeptide normally observed in reticulocyte incubations. A rapid processing event may occur in standard wheat germ incubations to release the 44K polypeptide from a nascent, elongating precursor. The 44K product did not arise because of limiting amounts of a particular tRNA species. Reticulocyte incubations with or without additional reducing agent showed comparable levels of all the processed TuMV RNA-specific products. We could detect no serological cross-reaction between any of the TuMV RNA-encoded products and antiserum raised against HPLC-purified helper component of tobacco vein mottling virus, another potyvirus.


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